1. Field of the Invention
The present invention relates to a diamond Schottky diode to be used for a rectifying device.
2. Description of the Prior Art
Diamond has a high thermal conductivity, an excellent stability against heat, and a large band gap. It is electrically insulating but becomes semiconducting upon doping. By the advent of the synthesis of diamond films by chemical vapor deposition (CVD), it has now become possible to grow B (boron)-doped p-type semiconducting diamond films and Si-doped n-type semiconducting diamond films.
Research and development efforts have been made to develop semiconductor devices employing such semiconducting diamond films, for example, a diamond Schottky diode used for a rectifying device which can be operated in a high electric power/high temperature region. A diamond Schottky diode is composed of a semiconducting diamond layer and a metal electrode. It has a higher Schottky barrier of 1.1 eV than the conventional one (0.8 eV) composed of a semiconducting silicon layer and a metal electrode made of aluminum or the like. Consequently, in the diamond Schottky diode, the reverse current due to thermionic emission is small under a reversed bias.
A diamond Schottky diode having such a cross-sectional structure as shown in FIG. 7 is disclosed in the literature (G. Sh. Gildenblat et al., Technical Digest of 1988 Int. Electron Device Meeting). It consists of a low-resistance silicon substrate 51 (resistivity: less than 1 .OMEGA..multidot.cm), a B-doped p-type semiconducting diamond layer 52, and a metal electrode 53 made of Au or Al.
The diamond Schottky diode is fabricated in the following procedure. A silicon substrate 51 is cut in adequate size and is then polished for about 30 minutes by diamond paste having an average particle diameter of about 1 .mu.m. A B-doped p-type semiconducting diamond layer 52 is formed on the silicon substrate 51 by microwave CVD. As a reaction gas, there is used a source gas of CH.sub.4 --H.sub.2 mixture (CH.sub.4 concentration: 0.5%) added with a doping gas of diborane B.sub.2 H.sub.6 diluted by H.sub.2. It takes about 7 hours to form the p-type semiconducting diamond layer 52 of about 2 .mu.m thick.
The conventional diamond Schottky diode fabricated as mentioned above is disadvantageous in that the reverse current is mainly due to recombination current and is greater than that due to thermionic emission. Thus it needs improvement in the reduction of reverse current.